Sound attenuating gas conduit



E. LUDLOW ETAL SOUND ATTENUATING GAS CONDUIT Dec. 17, 1963 4 Sheets-Sheet 1 Filed Aug. 21. 1961 M a W m ww mwfl 1 r LN T 0M W W 024 Dec. 17, 1963 E. LUDLOW ETAL 3,114,432

SOUND ATTENUATING GAS CONDUIT Filed. Aug. 21, 1961 4 Sheets-Sheet 2 mun!!! INVENTORS. I famwva Auaww 29 BY fi/vmm/m A! Zkw/n/ Arraweys Dec. 17, 1963 E LUDLQW A 3,114,432

I SOUND ATTENUATING GAS CONDUIT Filed Aug. 21, 1961 4 Sheets-Sheet 3 [NV EN T0125, EaMu/va L004. aw 9 By Bezvrnmw Ie WIN A 770/2 Me's s.

Dec. 17, 1963 LUDLQW ETAL 3,114,432

scum) ATTENUATING GAS CONDUIT Filed Aug. 21, 1961 4 Sheets-Sheet 4 INVENTORS. fomulvo Lumow y BCFIVJ'AMIN H. [kW/N f'mm idwg Arroeusvs.

United States Patent 3,114,432 SOUND ATTENUA'LING GAS CONDUIT Edmund Ludlow and Benjamin H. Irwin, Columbus, Ind., assignors to Arvin Industries, Inc, Columbus, Iud., a corporation of Indiana Filed Aug. 21, 1961, Ser. No. 132,910 12 Claims. (Cl. 181-59) This invention relates to a sound attenuating gas conduit for conveying, rand attenuating the noise level of, a moving gas stream, and which is well adapted for use with an internal combustion engine for conveying the exhaust gases thereof and silencing the noise level of said exhaust gases.

It is an object of the invention to provide such a sound attenuating gas conduit which will meet limited space requirements, which can be of light weight construction with its weight substantially uniformly distributed along its length, which will be less susceptible to certain types of corrosion than conventional gas-silencing systems,.and which may employ replaceable sound attenuating units. It is a further object of the invention to provide a sound attenuaitng gas conduit which may be formed from inexpensive metalatubing and sheet-metal stampings, which can be made to effect sound attenuation over a wide range of frequencies, and which will effect such sound attenuation with minimal back pressures. 1 a

It is a specific object of the invention to provide a sound attenuating gas conduit for the exhaust gas stream of an automotive vehicle, which will eliminate the need for bulky, expensive, and troublesome mufilers which are required in conventional exhaust silencing systems and which will eliminate the necessity of inserting silencing elements into a gas-carrying pipe as is required in certain in-line automotive exhaust-silencing systems.

The present invention is concerned with the construction of sound attenuating resonators mounted on, and acting in combination with, a conduit for conveying the exhaust gases away from an automotive engine. Such resonators may be constructed from inexpensive metaltubing and sheet-metal stampings, and may be constructed such that they are tuned to attenuate different and overlapping bands of sound wave frequencies. Many prior resonator constructions of the in-line type in which sound attenuation is carried out along the length of a gas-carrying conduit require the resonators to be disposed internally of the gas-carrying conduit. In some instances, such internal mounting creates sufficient back pressures within the gas-carrying conduit to necessitate the use of over-sized pipe. Such internal mounting also increases the difiiculty in mounting such resonators in the curved portions of the gas-carrying pipe. However, the instant invention overcomes these problems by the employment of resonators which may be formed from metal-tubing and sheet-metal stampings mounted externally of a gascarrying conduit at any desired location on said conduit, including the curved portions thereof. 7

In the employment of the invention as an exhaust system for an automotive vehicle, the exhaust manifold of the engine is connected to a first pipe to convey the exhaust gases emanating from said engine to the desired discharge point, as at the rear of the vehicle. This first pipe, usually with at least a part of the manifold, forms a conduit in which the exhaust sound produces standing wave pressure patterns wherein each of the several harmonic components of the standing waves have one or more distinct pressure points, that is, points of maximum sound pressure at particular locations along the conduit. The present invention is concerned with the construction of sound attenuating resonators mounted externally on the conduit in operative communication with these pressure 3,114,432 Patented Dec. 17, 1963 points and tuned to the frequencies producing such pressure points.

In accordance with one form of construction of said resonators, there is provided an elongated second pipe axially compartmented and secured to a first gas-carrying pipe. Each of the compartments in said second pipe con stitutes a resonator volume which is in operative communication with the gas-flow passage of said first pipe by means of an axially compartmented length of tubing secured to the outer walls of said first and second pipes. Each of the compartments in said length of tubing is provided with an opening disposed in alignment with an opening formed in said first pipe and an opening disposed in alignment with said second pipe, whereby each of said compartments in said length of tubing constitutes a resonator throat opera-tively interconnecting one of said reconator volumes to the gas-flow passage of said first pipe so that each of said throats and volumes will attenuate the noise level of the ex haustgases moving through said gas-flow passage.

Other obieots and features of the invention will become apparent from the more detailed description which follows and from the accompanying drawings in which:

FIG. 1 is a fragmentary isometric view of a sound attenuating exhaust system embodying our invention;

FIG. 2 is an enlarged fragmentary longitudinal section of the sound attenuating conduit shown in FIG. 1 and taken on the line 2-2 of FIG. 3;

FIG. 3 is a vertical section taken on the line 3 -3 of FIG. 2;

FIG. 4 is an isometric view of the resonator throatforming member shown in FIG. 2;

FIG. 5 is a fragmentary isometric view of a modified form of our sound attenuating gas conduit, and showing portions thereof broken away;

PEG. 6 is a vertical section taken on the line 6--6 of FIG. 5; p

FIG. 7 is a fragmentary isometric view of a different embodiment of the sound attenuating gas conduit shown in FIG. 5, and showing portions thereof broken away;

FIG. 8 is a vertical section taken on the line 8- 8 of PEG. 7;

FIG. 9 is a fragmentary isometric view of a modified form of our. sound attenuating gas conduit, and showing portions thereof broken away;

FIG. 10 is a vertical section taken on the line 10 -10 of FIG. 9;

FIG. 11 is a fragmentary isometric view of a different embodiment of the sound attenuating gas conduit shown in FIG. 9, and showing portions thereof broken away; and

FIG. 12 is a vertical section taken on the line 12-12 of FIG. 11.

This invention is particularly well adapted for use with an internal combustion engine in an automotive vehicle to silence the exhaust gases emanating from said engine and to convey them to a suitable discharge point. The

essential feature characterizing this inventionis the combination of a pipe for conveying such gases from the engine to a suitable discharge point and the construction of one or more resonators mounted externally on said pipe for attenuating the noise level of the gases passing therethrough.

These resonators are formed from lengths of metaltubing and sheet-metal stampings which are constructed so as to form resonator volumes and throats tuned to the desired sound wave frequencies, with said throats operatively interconnecting said volumes to the gas stream whereby said resonators will attenuate the noise level of the exhaust gases moving through said pipe. Because our resonators are formed from relatively small sheetmetal stampings and small diameter pipes and tubing, the overall weight of the system will be minimized, as will the cost of such system. Further, because of their relatively small size and external mounting, the resonators may be easily mounted on the pipe in substantially any desired location, including the curved portions of said pipe. The small size of the resonators also permits them to be mounted on the pipe in any desired circumferential position to thus obviate mounting them on the bottom of the pipe in a position in which they would tend to trap condensed corrosive materials. As will be obvious, the external mounting of the resonators prevents said resonators from creating any back pressures within said pipe, thus permitting said pipe to have a smaller diameter than conventional exhaust and tail pipes and pipes employing internally mounted in-line resonators, resulting in a reduction in both the Weight and cost of the system.

in theoperation of a conventional internal combustion engine in an automobile, the combustion of fuel within the cylinders produces a substantial volume of hot exhaust gases which are exhausted with substantial noise into the exhaust manifolds mounted on the engine in communication with the cylinder exhaust ports. The frequencies of the sound waves in such exhaust gases extend over a wide range, such as from about cycles per second to about 5,00%) cycles per second, with the lower frequencies largely representing the fundamental and lower harmonics determined by the length of the exhaust conduit. In many exhaust systems it is the lower range of frequencies, i.e., frequencies below 200 cycles 'per second, that are the most difiicult to attenuate and produce the most objectionable noises, especially since it is in this low frequency range that the firing frequencies of the engine coincide with and augment the natural resonant frequencies of the exhaust system itself.

The lower frequencies are particul-raly difficult to silence when the engine is propelling the vehicle at a rate of speed of from about 20 miles per hour to about 50 miles per hour. At these speeds rnost engines fire at frequencies below 200 cycles per econd, the range in which the fundamental and first overtone of substantially all silencing systems fall. Generally, if the engine is propelling the automobile at a speed slower than about 20 miles per hour, its firing frequencies will be well below the fundamental frequency of the silencing system and thus will not coincide with nor augment the natural resonant frequency of the exhaust system itself to any appreciable extent. And if the engine is propelling the automobile faster than about 50 miles per hour, its firing frequencies will generally be higher than the first overtone of the exhaust system. Also, the natural road noises at these higher speeds are more predominant than the exhaust gas noises.

In many conventional mufilers these lower frequencies are quite dihicult to attenuate because the large size of the mufflers prevents them from being positioned in the exhaust system on the under-side of the vehicle to act upon and attenuate these low frequencies.

Our invention is adapted to attenuate the exhaust noises incident to the operation of an internal combustion engine over a wide range of sound wave frequencies, including the troublesome frequencies below 290 cycles per second, by passing the exhaust gases of said engine through an exhaust conduit having a plurality of resonators mounted along'its length in any desired location, including the curved portions of said pipe. The resonators may be tuned to attenuate different and overlapping bands of frequencies. While resonators in accordance with our invention may be used alone to effect attenuation of the exhaust gas noises, they may be used in combination with conventional mufflers, or may be incorporated within otherwise conventional mulfiers as acoustical mufiier components, or used in combination with acoustical liners d employed in the manifold or in self.

The embodiment shown in FIG. 1 comprises a pipe ll adapted to be connected at one end to an exhaust manifold of-an internal combustion engine by a conventional mounting flange 14 with its opposite end open to the atmosphere. Conveniently, the pipe It) need not have a diameter any greater than the diameters of the exhaust and tail pipes used in a conventional exhaust system, which normally fall in the range of from about one three quarters to about two and one-half inches. But, it may have a larger diameter, say as large as four inches, the diameter of exhaust and tail pipes in trucks, busses, and other large vehicles. The pipe It) may be a unitary length, as illustrated, or it may be in the form of a plurality of short interconnected lengths of pipe.

The exhaust gases moving through the pipe 10 are silenced by the resonators illustrated in FIGS. 2 and 3. As shown, such resonators are formed from a second pipe is normally having a diameter smaller than the pipe 10 and a series of sheet-metal stampings 17, said pipe 16 extending generally parallel to the pipe it As shown in FIG. 2, a series of sheet-metal stampings are inserted within the pipe 16 and constitute bafile plates 18 which compartment said pipe intoa series of axially extending resonator volumes 20. The spacing between the baffle plates 18, and thus the size or capacity of the resonator volumes ill? will be determined by the frequency to which the individual resonators are tuned, as will be more fully explained hereinafter. As long as the bafile plates 18 are not disposed at or immediately adjacent a bend, the pipe 16 may be contoured and bent into any desired configuration to correspond to that of the gas-carrying pipe 16?. This permits the two pipes to fit closely adjacent to the under-carriage of an automotive vehicle, irrespective of the contour of said under-carriage, so that the exhaust system will meet extremely limited space requirements and give a substantial degree of vertical clearance on the underside of the vehicle.

As shown in FIGS. 2 and 3, one of sheet-metal stampings 17 is mounted on the pipes lit and 16 in association with each of the resonator volumes 20. The stamping illustrated comprises an upper plate portion 21 rigidly secured along its edges, as by welding, to the pipes 19 and 16. At each of its ends, the stamping 17 is provided with a generally V-shaped downturned flange 22 whose edges are curved to abut the adjacent outer walls of the pipes lit. and 16 along the lengths of said flange edges. In this manner, each of the stampings 17, together with the pipe wall portions lying within the extent of the pair of flanges 22 on. each of said stampings, forms a resonator throat 23. The edges of the flanges 22 are rigidly secured along their lengths to the outer walls of the pipes 10 and id to seal the ends of the throat 23 and rigidly interconnect the pair of pipes. Each throat 23 is in operative communication with the gas-flow passage of the pipe Ed by an opening 24 formed in the pipe 13 and in opeartive communication with its respective resonator volume 29' by an opening 25 formed in the pipe 16. As Will be apparent, each pair of openings 24 and 25 must lie within the extent of the end flanges 22 on each of the stampings 17. Each of the throats 23 operatively interconnects its resonator volume 20 with the gas-flow passage of the pipelll so that the resonators formed by said throats and volumes will attenuate the noise level of the g ses passing through said pipe 10.

As an alternative of the plurality of stampings 17, a single elon ated plate may be employed, with said plate having a series of axially spaced depending V-shaped members corresponding to the flanges 22 which compartment the space underlying said plate and disposed between the gas-carrying pipe and resonator volume-forming pipe into a plurality of resonator throats.

In order that the system of resonators will attenuate a substantial range of sound wave frequencies in the exhaust the exhaust conduit itgases, it is necessary that the individual resonators be tuned with respect to the harmonic characteristics of the exhaust conduit and/ or the firing frequencies of the engine. The latter, at least in the troublesome range below 200 cycles per second, normally are correlated with the former so that in most instances the resonators are tuned to frequencies which constitute multiples of fundamental resonant frequency of the conduit. Such multiples may constitute whole number multiples (for example, 1, 2, 3, etc.) in which case the resonators will be be tuned to the various harmonics of the conduit, and such multiples may also constitute mixed number multiples (for example, 1 /2, 2 /2, etc.) in which case the resonators will be tuned to fractional components of the conduit harmonics. Desirably, the resonators are tuned to both the whole number multiples and mixednumber multiples of the fundamental resonant frequency of the conduit, and are thus correlated with, and responsive to, both the harmonic conduit frequencies and the firing frequencies of the engine when said engine is propelling a vehicle at speeds in the rangeof from about 20 mph. to about 50 mph. While each resonator attenuates to the maximum degree the particular frequency to which it is tuned, it will, of course, attenuate to a lesser extent a limited band of frequencies on either side of that particular frequency, and willeifect some attenuation of substantially all frequenices.

Tuning of the resonators may be effected by adjusting the conductivity of the resonator throat with respect to the size or capacity of the resonator volume. The formula for calculating such tuning may be represented by the formula:

U Go -m v".

where f is the frequency to which the resonator is to be tuned, C is the speed of sound in inches per second at the temperature of the medium, V, is the capacity of the resonator volume, and C is the conductivity of the resonstor throat calculated from the formula:

where r is the radius of the throat and h is the length of the throat. Where the throats are non-circular, as in the case of the resonators shown in FIGS. 13, their conductivity may be calculated by the above formula using their cross-sectional area instead of quantiy 1rr and the mean radius of their cross-section instead of the quantity 11'). Thus, tuning of the resonators shown in FIGS. 1-3 can be effected by controlling the diameters of the pipe 16, the spacing between the baffle plates 18, the width of the stampings 17, and/or the spacing between the fianges 22. V

The fundamental resonant frequency of the exhaust conduit with which the frequency of the resonators are to be co-ordinated depends upon the speed of sound, and as shown by the first formula set forth'aboye, the frequency of a resonator likewise depends upon the speed of sound. Since the speed of sound varies with temperature, a temperature gradient between the resonator throats and exhaust gases will interfere with the co-ordination necessary for the resonators toachieve their maximum attenuation. These changes in the speed of sound resulting from changes in temperature of the medium in which the sound Waves are carried will also cause the frequencies of the sound waves to change, the degree of frequencychange depending upon the temperatures and frequencies involved. In our exhaust conduit, the temperature of the exhaust gases from the engine to which the conduit is connected will vary over a wide tempera ture range of from about 200 '-F., when the engine is cold, to a temperature of about 1,700 E, when the engine is hot.

In a typical example of our invention using an exhaust conduit having a first overtone (second harmonic) of cycles per second, we have found that the first over -tone shifted to' 106 cycles per second when the engine was propelling the vehicle 2 5 miles per hour, and that it was shifted to 121 cycles per second when the engine was propelling the vehicle 50 miles per hour. This frequency shifting resulted from the increased temperatures of the exhaust gases. Furthermore, at 25 miles per hour the engine had a firing frequency of about 80 cycles per second, and a firing frequency of 120 cycles per second at 50' miles per hour. As will be apparent, in the lower frequency range, i.e., below 200 cycles per second, the firing frequencies of the engine coincide with and augment the natural resonant frequencies of the exhaust conduit making these lower frequency ranges extremely difficult to attenuate.

Although the external mounting of the throats 23 causes them to be subjected to air wash during movement of the vehicle,,said throats have a common wall (the pipe 10) with the gas-flow passage to thus permit, to a limited degree,. their temperatures to follow the temperatures of gases moving through said passage. Furthermore, it is possible to approximate the temperature of the exhaust gas stream in the pipe 10 at the positions at which the throats 23 are coupled to the gas stream. Thus, the resonators may be tuned to effect a high degree of attenuation irrespective of the temperature of the gas stream at the points where the throats 23 are coupled thereto.

Preferably, the resonators are tuned to attenuate the objectionable harmonics, or fractional components of said harmonics, in the gases in the conduit. Each of these harmonic components will have specifically 1ocated maximum sound-pressure points along the length of the conduit, the number of such pressure point-s and their location being a function of the particular harmonic component involved. F or example, the second overtone (third harmonic) will have three maximum pressure points along the conduit which will occur at points spaced from either end of the conduit by distances of one-sixth, onehalf, and fiye-sixths of the conduit-length. Each of the resonators will attenuate to the maximum degreethe particular harmonic, or fraction of a harmonic, to which it is tuned, if its throat opening is coupled to the gas stream at one of the points of maximum pressure of the harmonic or harmonic fraction for which it is tuned. While the resonators will effect maximum attenuation while their throats are located precisely at their maxi- -rnum pressure points, they will, of course, still operate at high attenuation etficiencies if their throats are located adjacent such pressure points. For example, we have found that a resonator will operate at not less than efficiency if its throat :opening is placed at any point 'lWillhin a distance from the true maximum pressure point equal to one-twentieth of the length of the sound wave producing the pressure point.

In general, such maximum pressure points are spaced from an end of the conduit by fractions L of the conduitlength according to the formula:

where n is the harmonic number for which the resonator is tuned, and m is every integer between and including 1 and n.

The above formula is used for calculating the locations of the warious sound-pressune points when the conduit and- 7 tions of the pressure points shift downstream a distance equal to from about 2% to about 4% of the wave length of the frequencies producing the various pressure points. The temperature gradient along the conduit from the exhaust manifold on the engine to the discharge end of said conduit is not uniform, and the locations of the pressure points toward the upstream end of the conduit will be shifted downstream to a greater degree than the locations of the pressure points toward the discharge end of the conduit. Thus, the resonators are tuned to attenuate the desired sound wave frequencies in the gases in the conduit and the above formula is employed to determine the positions that the resonator throats should open into the conduit. However, for the resonators to achieve maximum effectiveness, the resonators are mounted on the conduit with their throats opening into the conduit at points spaced downstream from the locations calculated by said formula by distances equal to about 2% to about 4% of the wave length of the frequencies to which the resonator s are tuned.

In some instances it may occur that a maximum pressure point will lie within a curved portion of the pipe lib. However, because of the construction of the resonatorforrning pipe lo and the throat-forming stampings l7,

resonators maybe provided within the extents of such curved portions, as shown in FIG. 1. This permits the resonators to be mounted on the pipe it at any desired location, even such curved portions, to thus provide an efficient and effective sound attenuating system for attenuating the various frequencies and bands of frequencies, irrespective of the sound wave pressure patterns of the pipe 10. Furthermore, this external mounting of the resonators on the pipe 16 permits the exhaust gases to move through the pipe in with an uninterrupted flow to thus provide sound attenuation of said gases without the creation of any back pressures Within the pipe iii except, of course, for the normal pressure created by the frictional drag of the side walls of said pipe.

A modified form of our sound attenuating gas conduit is illustrated in FIGS. 5 and 6, wherein there is provided a first pipe 27 forming a gas-flow passage. A second pipe 28 is rigidly secured to the outer wall or" the pipe 27 and extends axially thereof and has disposed within it a plurality of axially spaced baftle plates 29 which compartment said pipe into a plurality of resonator volumes 3h. Wedged between the pipes 27 and 28 is a length of small diameter tubing 31 having a generally V-shaped crosssection whereby its outwardly presented walls will mate with the adjacent outer walls of the pipes 27 and 28. The tubing 31 is rigidly secured to the walls of the pipes 27 v and 28 to mount it thereon and to further rigidly interconnect said pair of pipes. A series of axially spaced bafile plates 32 are disposed Within the tubing 31 and compartment said tubing into a series of elongated resonator throats 33. Said throats are disposed in operative communication with the gas-flow passage of the pipe 27 as by forming aligned openings 34 and 35 in the tubing 31 and pipe 27, respectively, and in operative communication with the resonator volumes Bit by forming aligned openings 36 and 37 in the pipe 28 and tubing 31, respectively. As will be understood, each pair of the pairs of openings 34-735 and 36-37 lie within the axial extent of one of the volumes 39 so that each of the volumes 30 is operatively interconnected through its associated throat to the gas-flow passage of the pipe 27 whereby the resonator throats and volumes will attenuate the noise level of the gases passing through said pipe 27. v

A modified embodiment of the sound attenuating gas conduit shown in FIGS. 5 land 6 is shown in FIGS. 7 and 8, and differs from the modification of FIGS. 5 and 6 in the cross-sectional configuration of the throat-forming tubing and its orientation with respect to the gas-carrying pipe and volume-forming pipe. The modification shown in FIG. 7 includes a first pipe 27' defining a gas-flow passage. A second pipe 23' extends alongside the pipe 27',

conveniently in parallelism therewith. A series of axially spaced bafiled plates 29' are disposed within the pipe 28' and compartment said pipe into a plurality of axially extending resonator volumes 39.

The pipe 23' is interconnected to the pipe 27' by a length of small diameter tubing 31 formed into a generally rectangular cross-section with concave opposed side walls adapted to abut the adjacent outer walls of the passages 27 and 28. The concave side walls of the tubing 31' are rigidly secured to the outer walls of the pipe 27 and 28 to thus rigidly interconnect said pipes. A plurality of axially disposed bafile plates 32 are disposed witliin the tubing 31' and compartment said tubing into. a plurality of axially extending resonator throats 33. Each of the throats 33 is operatively connected to the gasfiow passage of the pipe 27' by aligned openings 34 and 35' formed in the tubing 31 and pipe 27', respectively, and to a resonator volume 3th by aligned openings 36' and 37' formed in the pipe 28' and tubing 31', respectively. Each pair 'of the pairs of openings 34'-35' and 3637 are disposed within the axial extent of one of the resonator volumes 30 whereby each of said volumes and its associated throat 33 will attenuate the noise level of the gases passing through the pipe 2'7.

A modified embodiment of our invention is illustrated in FIGS. 9 and 10, and comprises a first pipe 40 defining a gas-flow passage and second pipe 42 generally parallel therewith and rigidly connected thereto. A plurality of axially spaced bafile plates 4-4 are disposed within the pipe 42 and compartment it into a plurality of axially extending resonator volumes 45. Each of the volumes 45 is operatively connected to the gas-fiowpassage of the pipe 4'15 by a length of small diameter tubing 46 rigidly secured to the pipes 449 and 42 and having its ends received in openings formed in said pair of pipes. Each of the lengths of tubing 46 thus forms a resonator throat operatively interconnecting one of the volumes 45 with the gasfiow passage whereby said throats and volumes will attenuate the noise level of the gases moving through the pipe ill.

A modified embodiment of the sound attenuating gas conduit shown in FIGS. 9 and 10 is shown in FIGS. 11 and 12. The embodiment illustrated in FIG. 11 comprises a first pipe 4% defining a gas-flow passage and a second pipe 42' generally parallel therewith and rigidly connected thereto. A plurality of bafiie plates 44' are disposed within the pipe 42 and compartment it into a plurality of axially extending resonator volumes 45'.

Each of the volumes 45' is operatively connected to the gas-flow passage of the pipe 49' by a pair of resonator throat-forming stampings 47 and 43. As shown in PEG. 12, the stamping 47 spans the pipes 40' and 42 and is provided with a pair of extruded openings 49 received in, and connected to, openings formed in said pipes. The stamping 43 has a bead 5% formed therein and has its marginal edges rigidly secured to the margins of the stamping 47 whereby the pair of stampings 47 and 48 form a resonator throat 5i operatively interconnecting one of the volumes 45 with the gas-flow passage. In the illustrated embodiment, the margins of the stamping 47 are secured to the outer Walls of the pipes 40' and 42', and said stamping may thus further serve as an interconnecting means for said pair of pipes.

While we have shown the resonator volume-forming pipes and gas-carrying pipes as having circular cross-sections, it is to be understood that either of said pipes may have any desired cross-sectional configuration. It is also within the spirit and scope of our invention to employ more than a single resonator volume-forming pipe and throat-forming tubing or'set of stampings in association with a gas-carrying pipe. Indeed, in certain applications, it may be desirable to have a plurality of resonators attenuating the same sound wave frequencies at the single sound-pressure point of that frequency. In which case, it is merely necessary to cluster a plurality of axially extending resonator volume-forming pipes and their associated resonator throat-forming members about the outer wall of the gas-carrying pipe, with the throats of said resonators opening into the gas-carrying pipe at or adjacent said pressure point. it also contemplated that the unitary axially extending volume-forming pipes and throatforming tubing may comprise a plurality of shorter lengths of pipe and tubing, and need not extend for substantially the complete length of the gas-carrying pipe.

For purposes of simplicity of description, we have only described our invention for use in an exhaust system for an engine. However, it may, of course, also be used on the intake side of an internal combustion engine for supplying and silencing the gas intake fiow to the engine, or for many other silencing applications.

We claim:

1. in a sound attenuating gas conduit for conveying, and attenuating the noise level, of a moving gas stream, an elongated conduit forming a gas-flow passage, one or more axially extending closed end pipe sections fixedly interconnected to the outer wall of said conduit along axially extending lines of interconnection equal to substantially the entire axial extents of said pipe sections and each forming a resonator volume, said conduit and pipe sections being interconnected in close proximate relationship with each other, and means secured to the outer walls of said conduit and pipe sections in operative association with openings formed therein to form a resonator throat interconnecting each of said volumes with said gas-how passage whereby each of said throats and volumes will attenuate the noise level of the gas stream moving through said gas-dew passage.

2. In a sound attenuating gas conduit for conveying, and attenuating the noise level, of a moving gas stream, an elongated conduit forming a gas-flow passage, an elongated pipe fixedly interconnected to the outer wall of said conduit along axially extending lines of interconnection equal to substantially the entire axial extent of said pipe and generally parallel therewith, said conduit and pipe being interconnected in close proximate relationship to each other, a plurality of axially spaced halide plates in said pipe compartmenting said pipe into a plurality of resonator volumes, and means secured to the outer walls of said conduit and pipe and operatively associated with openings formed-therein to form a plurality of resonator throats, each of said throats interconnecting one of said volumes to said gas-flow passage whereby said resonator throats and volumes will attenuate the noise level of the gas stream moving through said gas-flow passage.

3. The invention as set forth in claim 12 in which said means comprises an elongated plate bridging the space between adjacent portions of the outer walls of said conduit and pipe, and a plurality of axially spaced members extending from said plate into the space between said conduit and pipe with the edges of said members abutting the walls of said conduit and pipe, the edges of said plate and said members being rigidly secured to said conduit and pipe along the length of said plate and member edges.

4. The invention as set forth in claim 2 in which said means comprises a plurality of elongated plates each of which is rigidly secured along its longitudinal edges to said conduit and pipe, each of said plates at its opposed ends having generally V-shaped flanges whose edges are rigidly secured to said conduit and'pipe, each of said plates being mounted on said conduit and pipe in positions such that a pair of said openings in said conduit and pipe are disposed between its pair of flanges.

5. The invention as set means comprises a length of tubing having a substantially smaller cross-section than said resonator volume-forming pipe, a plurality of axially spaced baflle plates mounted in said tubing compartmenting the same into a plurality of resonator throats, said tubing within the extent of each forth in claim 2 in which said 10 of said throats having openings disposed in alignment with said openings in the conduit and pipe.

6. The invention as set forth in claim 5 in which said tubing has a pair of wall surfaces curved to abut portions of said adjacent walls of said conduit and pipe in face-toface contact.

7. The invention as set forth in claim 5 in which said tubing is' interposed between said conduit and pipe in an abutting face-to-face relationship and rigidly interconnects said conduit and pipe.

8. The invention as set forth in claim 2 in which said eans comprises a plurality of open-ended passage-forming members each of which has one of its ends received in one of said openings in said conduit and its opposite end received in one of said openings in said pipe.

9. The invention as set forth in claim 2 in which said means comprises a pair of sheet-metal stampings rigidly secured together with portions of their walls in spaced relation to each other, and one of said stampings having 7 a pair of openings formed therein and disposed in open communication with openings formed in said conduitand pipe.

10. The invention as set forth in claim 9 with the addition that the margins of said one of said stampings are rigidly secured to the outer walls of said conduit and pipe, and said openings in said one of said stampings are extruded openings projecting into the openings in said conduit and pipe.

11. An exhaust silencing system for an internal combustion engine, comprising a pipe for connection to the engine to receive the exhaust gasesthereof and to convey such gases to a discharge point, said pipe forming a gas conduit wherein the exhaust gas sound produces a plurality of distinct sound-pressure points at particular locations along the conduit, and a plurality of resonators disposed adjacent said pressure points, each of said resonators comprising a closed end pipe section generally parallel with said conduit and fixedly interconnected to the outer wall thereof along axially extending lines of interconnection equal to substantially the entire axial extent of said resonator to form a resonator volume, said pipe and resonators being interconnected in close proximate relationship to each other, and means secured to the outer Walls of said conduit and pipe section and operatively associated with openings formed in said conduit and pipe section to form a resonator throat, said opening in said conduit being formed therein adjacent the pressure point of the frequency to which the associated throat and volume are tuned whereby said resonator will preferentially attenuate the noise level of said frequency.

12. Th invention as set forth in claim 11 with the addition that adjacent at least one of said sound pressure points a plurality of said resonators tuned to the frequency producing said pressure point are fixedly interconnected to the outer wall of said conduit, and said conduit is provided with a plurality of openings thereat each of which opens into one of the throats of said plurality of resonators.

References Cited in the file of this patent UNITED STATES PATENTS (Addition to 873,027) 

1. IN A SOUND ATTENUATING GAS CONDUIT FOR CONVEYING, AND ATTENUATING THE NOISE LEVEL, OF A MOVING GAS STREAM, AN ELONGATED CONDUIT FORMING A GAS-FLOW PASSAGE, ONE OR MORE AXIALLY EXTENDING CLOSED END PIPE SECTIONS FIXEDLY INTERCONNECTED TO THE OUTER WALL OF SAID CONDUIT ALONG AXIALLY EXTENDING LINES OF INTERCONNECTION EQUAL TO SUBSTANTIALLY THE ENTIRE AXIAL EXTENTS OF SAID PIPE SECTIONS AND EACH FORMING A RESONATOR VOLUME, SAID CONDUIT AND PIPE SECTIONS BEING INETERCONNECTED IN CLOSE PROXIMATE RELATIONSHIP WITH EACH OTHER, AND MEANS SECURED TO THE OUTER WALLS OF SAID CONDUIT AND PIPE SECTIONS IN OPERATIVE ASSOCIATION WITH OPENINGS FORMED THEREIN TO FORM A RESONATOR THROAT INTERCONNECTING EACH OF SAID VOLUMES WITH SAID GAS-FLOW PASSAGE WHEREBY EACH OF SAID THROATS AND VOLUMES WILL ATTENUATE THE NOISE LEVEL OF THE GAS STREAM MOVING THROUGH SAID GAS-FLOW PASSAGE. 